Notifications should respect Permission Schemes associated with project.

For example, when moving an issue to another project in which the reporter does not have access, the reporter will still receive email notifications of issue updates.

At present, the 'Comment Viewable' level is respected. In the long term, the best solution would most likely take a hierarchical form - with each level over-riding its parent level - e.g.:

Global Permissions
Project Permissions
'Comment Viewable' permissions.